Overrunning clutches are widely used in order to allow relative rotation in one direction only between a pair of rotatable members, such as clutch races. Such overrunning clutches generally include a plurality of wedging elements, such as cylindrical rollers, and a cage that provides the basic structural framework of the clutch, retaining the wedging elements as well as providing a mount for energizing springs. While the wedging elements and the races are metal, it is often preferred that the cage itself be made of a moldable plastic material. This is particularly true if the cage is what is known as a concentric control cage. Such a cage includes support portions, often called journal blocks, that fit very closely within the annular space defined by the confronting surfaces of the races. Thus, when the clutch overruns, selected surfaces of the support portions may ride upon the surface of the more rapidly rotating race, and the races will thus be maintained in coaxial relation to one another without the need for separate bearings. Even with clutch cages that are not concentric control cages, the cage will generally fit closely within the annular space, because the cage will be tied to one of the races, unlike a bearing cage.
There are drawbacks, however, to forming a cage of moldable plastic material. The most serious drawback is that the plastic material generally has a thermal coefficient of expansion and contraction far greater than that of the metal races. Thus, as the metal races expand or contract with increasing or decreasing temperature, the cage will attempt to expand or contract to a significantly greater degree. However, since the cage is confined by definition within the annular space, the cage may be forced into the outer race as the temperature increases, or into the inner race as temperature decreases. This potentially may cause the cage to buckle into the race that it is tied to, or cause the surface of the cage that is supposed to slide on the other race to bind. Another potential drawback is that plastic will generally have less wear resistance than the metal wedging elements. In the case of cylindrical rollers, the ends of those rollers may potentially wear on the side walls of a plastic cage, especially where misalignment between the races may cause roller skew. However, the benefits of plastic, such as its moldability, light weight, and desirable frictional characteristics all dictate that it be used wherever possible. Therefore, it is worthwhile to attempt to overcome these drawbacks.
The U.S. Pat. No. 4,570,762 to Husmann discloses a roller clutch cage that attempts to solve the problem of thermal coefficient differential referred to above. It is known to increase circumferential flexibility of a bearing cage by adding alternating relieved portions to the side rails thereof, as shown in the foreign patent document No. 1264167, dated 3/1968, from the Federal Republic of Germany. Husmann takes a different approach, however. The cage there disclosed, as seen in FIG. 2, has axially spaced side rails 4 and 5, each of which has a circumferentially spaced series of so called resilient portions 26 and 27. These resilient portions, it is claimed, facilitate the circumferential elastic deformation of the cage, and thereby permit displacement of the individual cage chambers relative to one another. However, it is quite clear from an analysis of an actual sample of that cage that it is in fact not noticably more flexible than a conventional cage with solid side rails. This is because each of the side rails, despite the presence of the so called resilient sections, still is circumferentially continuous. There is still plastic material continuously all the way around each side rail. Therefore, both side rails will still respond to temperature changes essentially as would a conventional side rail. There are other drawbacks to the Husmann design, as well. The embodiment disclosed has two parts, and is not moldable as a unitary structure. While it is recited that the cage could be molded as a unitary structure with "somewhat greater molding and machine effort", it is quite clear that the number of movable molding elements necessary to mold such a cage would have to be equal to at least the number of individual cage pockets plus two. This is impractical, but a multi-part cage is undesirable as well. Furthermore, the cage pockets of the Husmann design are all plastic, and therefore subject to excessive roller wear in certain applications.